add user rename endpoint to admin api (#22789)

this is a simple endpoint that adds the ability to rename users to the
admin API.

Note: this is not in a mergeable state. It would be better if this was
handled by a PATCH/POST to the /api/v1/admin/users/{username} endpoint
and the username is modified.

---------

Co-authored-by: Jason Song <i@wolfogre.com>

routers/api/v1/swagger/options.go

@@ -48,6 +48,9 @@ type swaggerParameterBodies struct {
 	// in:body
 	CreateKeyOption api.CreateKeyOption
 
+	// in:body
+	RenameUserOption api.RenameUserOption
+
 	// in:body
 	CreateLabelOption api.CreateLabelOption
 	// in:body